The present invention relates to a manually operated working tool having an inductive metal detector assembly having at least one excitation coil arrangement and evaluation means, wherein the inductive metal detector system has a means for generating an alternating current for the excitation coil arrangement having at least two consecutive frequencies fn from a starting frequency f0 to an end frequency fmax. This type of working tool can, for example, be configured as a bolt setting tool.
In the case of manually operated working tools in steel to steel fastening applications such as, for example, in the fastening of sheet steel to steel panels.
EP 0 366 221 A2 discloses a manually operated working tool, especially a drilling machine, on which a metal detector is arranged for detecting metal parts located in the substrate. A coil arrangement is arranged in the metal detector, with which a spatially rotating alternating current field is generated by rotation of the coil arrangement or by alternating current supply to the coil arrangement. When this is done, the frequency of the alternating electrical current for operating the coil arrangement is held constant. The variation of the electrical energy pulled through the coil arrangement is measured.
A metal concealed in the substrate can be detected by virtue of this type of coil arrangement and, if required, its orientation in the substrate determined. If, however, the substrate is comprised of metal such as, for example, the fastening of sheet steel to steel beams, the situation of the beams can no longer be resolved because of the influence of the sheet steel.
U.S. Pat. No. 5,500,783 discloses a method and a circuit for automatically triggering the operation for setting a fastening element onto a substrate and a support. In the circuit, a comparator receives a first signal from a sensor and generates an intermediate signal, if a pre-defined condition between the first signal and a pre-defined value is fulfilled. A control device generates a control signal after receiving the intermediate signal of the sensor and the primary signal. A fastening element is driven by an actuator into the surface and the support as a consequence of the control signal. The structure of the sensor and signal processing is not described in U.S. Pat. No. 5,500,783.
DE 198 47 688 C2 discloses a method and the sensor based on said method for detecting foreign bodies in a medium, in particular concrete, tiling, plaster or wood using radar, by a pulse radar or a stepped frequency radar. This method provides a radar wave of very short duration that is radiated into the medium using a transmitting/receiving antenna for picking up the radar signal reflected in the medium and after pre-processing of a signal evaluation and assessment, which is based on an algorithm, and renders identifiable the differences in the signal form, for example of a performance range compared with stored comparison values of a sample spectrum with subsequent evaluation of the comparison by correlation for determining deviations vis-a-vis pre-definable critical or limit values of a correlation factor.
In this case, the drawback in steel to steel applications is that the radar waves generated are already reflected to a significant degree by the first metal layer and a metal element situated behind it is not recognized.
A very high power output of the radar detector is required to achieve passage through the front metal layer such as, for example, a metal sheet. In this case, realization of such a detector system in a manually operated working device without a mains connection is not possible. In addition, the microwave generator for the device is relatively expensive.
DE 44 05 648 A1 discloses, as is already well-known, arranging an inductive or capacitive sensor (not more precisely defined) at the front of a fluid-driven driving tool and coupling with a controller device.